Visualization and quantification of two-phase flow in transparent miniature packed beds

Optical microscopy was used to visualize the flow of two phases [British Petroleum (BP) oil and an aqueous surfactant phase] in confined space, three-dimensional, transparent, natural porous media. The porous media consisted of water-wet cryolite grains packed inside cylindrical, glass microchannels, thus producing microscopic packed beds. Primary drainage of BP oil displacing an aqueous surfactant phase was studied at capillary numbers that varied between ${10}^{-6}$ and ${10}^{-2}$. The confinement space had a significant effect on the flow behavior. Phenomena of burst motion and capillary fingering were observed for low capillary numbers due to the domination of capillary forces. It was discovered that breakthrough time and capillary number bear a log-log scale linear relationship, based on which a generalized correlation between oil travel distance $x$ and time $t$ was found empirically.

Figure 1

A scheme of silt grain particles between sand grains.

Figure 2

(a) Scheme of a microchannel packed bed. (b) Snapshot of cryolite particles inside the channel.

Figure 3

From top to bottom, snapshots of the displacement process for $\mathrm{Ca}=5.67\times {10}^{-5}$ at time $t=0$, 101.4, 113.5, and 129.3 s (near breakthrough). The dark phase is oil, while the bright phase is Tween 80 aqueous solution. Flow direction is from left to right.

Figure 4

From top to bottom, snapshots of the displacement process for $\mathrm{Ca}=5.06\times {10}^{-3}$ at time $t=0$, 0.02, 0.051, and 0.07 s (near breakthrough). The dark phase is oil, while the bright phase is Tween 80 aqueous solution. Flow direction is from left to right.

Figure 5

From top to bottom, snapshots of the displacement process for $\mathrm{Ca}=5.62\times {10}^{-6}$ at time $t=0$, 801, 1246, and 1505 s (near breakthrough). The dark phase is oil, while the bright phase is Tween 80 aqueous solution. Flow direction is from left to right.

Figure 6

Oil travel distance as a function of time at different capillary numbers. For comparison, the position is normalized by maximum length $L$, and the travel time is normalized by breakthrough time $t_{\mathrm{b}}$.

Figure 7

Breakthrough time as a function of capillary number Ca. $t_{\mathrm{bc}}$, the calibrated breakthrough time that has the unit of second, is defined as $t_{\mathrm{bc}}=t_{\mathrm{b}}/L\times L_0$, where $L_0$ is equal to $1400\mu \mathrm{m}$.

Figure 8

A plot of ${\log }_{10}\frac{x}{{\left(t{\mathrm{Ca}}^{1.54}\right)}^7}$ against ${\log }_{10}\left(t{\mathrm{Ca}}^{1.54}\right)$ for all capillary numbers. $\frac{x}{{\left(t{\mathrm{Ca}}^{1.54}\right)}^7}$ is in $\mu \mathrm{m}/{\mathrm{s}}^7$ and $t{\mathrm{Ca}}^{1.54}$ is in seconds. All data fall into the green (lighter gray) straight-line region, the center of which is represented by the dotted line. In addition, the gray (darker gray) region, with the dash-dotted line as the center, is the area where all data for $\mathrm{Ca}>{10}^{-4}$ collapse.